The chromatin of eukaryotic cells has a subunit structure containing nu bodies or nucleosomes. Each nucleosome contains eight histones, probably two each of H2a, H2b, H3 and H4. Part of this proposal involves a study of the interactions between these histones to see which interactions are essential and which, perhaps, are accidental. Histone Hl is external to the nucleosome. Part of this study involves the study of conformational changes of Hl and the interaction of the Hl subfractions with the non-histone chromosomal proteins of the high mobility group (HMG proteins). Part of this study involves an attempt to purify nicking-closing enzyme from calf thymus and study its interaction with Hl.